## Mathematica, 25 bytes Tally@#~MatchQ~{{_,2}..}& [Try it online!](https://tio.run/##RU7BCsIwDL3vKwTBg4S5pp1tD8J@QFDwLmU4Ntg8SC9Stl@fSbYhpS95yUvyhhDb1xBiV4e52V3mR@j7b7WfriHW7X1K6Qk45vl4mG@f7h2rY3OqUpYsKA0eEFRBYDhIyYAfIUuKihoEhRYkkE@wpiuTNpIWRekAEUqrnAfjcSMOnNAlX9pKZrN0ppsGGC1/XkJz22NaktYAI0UuWAtaUYHAkW9LKV34@8bFluHFMlCSU72Z5faS4nqYVdk4/wA) The `Tally` function returns a list of the form `{{element, count}, ...}`, which is then matched against a pattern that checks whether all `count` are 2.